Method and device for the production of an essentially continous fine thread

Abstract

The invention relates to a method and a device for the production of essentially continuous fine threads made of meltable polymers. The polymer melt is spun from at least one spin hole ( 5 ) and the spun thread is attenuated using gas flows which are accelerated to achieve high speeds by means of a Laval nozzle ( 6 ). As a result of the specific geometry of the melt hole ( 4 ) and the position thereof in respect to the Laval nozzle ( 6 ), the temperature of the polymer melt, the throughout per spin hole and the pressures determining the velocity of the gas flow upstream and downstream from the Laval nozzle ( 6 ) are controlled in such a way that the thread reaches an internal hydrostatic pressure before solidifying, whereby said thread bursts into a plurality of fine threads.

What is claimed is:  
     
       1. Method for the manufacture of essentially endless fine threads from meltable polymers, comprising the steps: 
       spinning polymer melt from at least one spin hole to form a thread,  
       passing the thread through a Laval nozzle, and accompanying the melt stream by a surrounding gas streams, wherein the spun thread is drawn by the gas streams which are accelerated to high speed by means of the Laval nozzle, and  
       controlling, with a given geometry of the melt hole and its position relative to the Laval nozzle, the temperature of the polymer melt, its throughput per spin hole and the pressures in front of and behind the Laval nozzle which define the speed of the gas streams in such a way that the thread before solidification thereof attains a hydrostatic pressure in its interior which is greater than the gas pressure surrounding it, such that the thread bursts and splits into a plurality of fine threads.  
     
     
       2. Method according to  claim 1 , wherein the gas flow around the at least one thread is laminar. 
     
     
       3. Method according to  claim 1 , wherein the space behind the Laval nozzle is at ambient pressure or, in case of further processing of the threads, is at a pressure slightly above ambient pressure, which is necessary for further processing. 
     
     
       4. Method according to  claim 1 , wherein the gas streams which draw the thread are at ambient temperature or a temperature caused by their supply. 
     
     
       5. Method according to  claim 1 , wherein the ratio of the pressures in the space above and below the Laval nozzle when using air is selected between 1.02 and 2.5, depending on the polymer, its throughput and melting temperature. 
     
     
       6. Method according to  claim 1 , wherein the thread emerging from the spin hole is heated by radiation in the region of the Laval nozzle. 
     
     
       7. Method according to  claim 1 , wherein a plurality of threads are spun and split, which are deposited to form a non-woven fabric or further processed into yarns. 
     
     
       8. Method for the manufacture of essentially endless fine threads from meltable polymers, comprising the steps: 
       spinning polymer melt from at least one spin hole to form a thread,  
       passing the thread through a Laval nozzle, and accompanying the melt stream by a surrounding gas streams, wherein the flow of the gas streams around the at least one thread is laminar, and wherein the spun thread is drawn by the gas streams which are accelerated to high speed by means of the Laval nozzle, and  
       controlling, with a given geometry of the melt hole and its position relative to the Laval nozzle, the temperature of the polymer melt, its throughput per spin hole and the pressures in front of and behind the Laval nozzle which define the speed of the gas streams in such a way that the thread before solidification thereof attains a hydrostatic pressure in its interior which is greater than the gas pressure surrounding it, such that the thread bursts and splits into a plurality of fine threads.  
     
     
       9. Method according to  claim 8 , herein the space behind the Laval nozzle is at ambient pressure or, in case of further processing of the threads, is at a pressure slightly above ambient pressure, which is necessary for further processing. 
     
     
       10. Method according to  claim 8 , wherein the gas streams which draw the thread are at ambient temperature or a temperature caused by their supply. 
     
     
       11. Method according to  claim 8 , wherein the ratio of the pressures in the space above and below the Laval nozzle when using air is selected between 1.02 and 2.5, depending on the polymer, its throughput and melting temperature. 
     
     
       12. Method according to  claim 8 , wherein the thread emerging from the spin hole is heated by radiation in the region of the Laval nozzle. 
     
     
       13. Method according to  claim 8 , wherein a plurality of threads are spun and split, which are deposited to form a non-woven fabric or further processed into yarns.